The invention relates to a quick response compact electronic medical thermometer according to the preamble of the independent patent claim 1.
It is known to use electronic thermometers for indicating the temperature of a patient for medical purposes. These compact electronic thermometers in the healthcare field generally take the form of a hand-held probe having an elongated shank portion therein. The elongated probe is especially configured for convenient oral, rectal or axillary use.
The probe is usually formed of a tube having a metal tip, within which the temperature-sensitive element is attached.
Since about 1985 the compact electronic medical thermometers brought some advantage due to easy readable display and quicker measurement time of about 60 to 90 seconds, compared to 3 to 5 minutes of traditional mercury thermometers. This measurement time delay is caused by the heat capacity of the probe and the fact that applying the entire probe to the patients tissue draws down the temperature of the tissue in the immediate region of the probe.
There have been several approaches to shorten the measurement time of compact electronic medical thermometers during the last 10 to 15 years.
E.g. U.S. Pat. No. 4,183,248 discloses an electronic thermometer probe which comprises two temperature sensors and a heater coil. The heater coil is used to thermally isolate the tip from the remainder of the probe, which eliminates long thermal time delays. They claim to reach a remarkable improvement of about 16 seconds measurement time.
U.S. Pat. No. 5,632,555 also discloses a medical thermometer which comprises a heater and a powerful and expensive microprocessor to adapt a prediction algorithm. The heater is used to bring the probe metal tip to a specific temperature when the probe is removed from a base housing. The predictive algorithm is to determine the final temperature before this temperature is effectively measured by the temperature sensor. They claim a measurement time of about 4 to 15 seconds.
All these known thermometers have certain drawbacks. Especially, thermometers having a built-in heater and/or expensive microprocessor with sophisticated circuitry are not suitable for home use, as these additional elements (heater, control means for the heater with high energy consumption, expensive microprocessor) lead to more expensive and bulky devices.
It is an object of the present invention to overcome the disadvantages of the prior art, especially to provide a quick response compact electronic medical thermometer for home use, which can be manufactured in an easy and economic way and which allows a faster measurement of the temperature of the patient, compared to conventional compact electronic medical thermometers.
According to the present invention, these objects are resolved with a quick response compact electronic medical thermometer according to the characterizing portion of independent patent claim 1.
The quick response compact electronic medical thermometer for measuring the temperature of a patient comprises a probe body which has a metal tip to contact with a patient""s tissue. A temperature sensor is mounted within the metal tip.
The temperature sensor is adapted to produce a signal representing the temperature of the metal tip. The probe body with the metal tip is especially intended for oral, rectal or axillary use. Any kind of known temperature sensors could be used, e.g. temperature sensitive resistors (thermistors).
The quick response compact electronic medical thermometer further comprises a display for indicating the temperature of the metal tip. Upon contact between the patient""s tissue and the metal tip, the displayed temperature of the metal tip approaches the patient""s temperature.
The inventors of the present invention have surprisingly found that the execution of a probe body with metal tip without additional heating and with a ratio between the length of the metal tip and the diameter of the metal tip of at least three, preferably five, leads to a considerable reduction of the measurement time. According to the present invention, the metal tip surrounds a substantially hollow cavity filled with air or a gas or a material having a comparable thermal capacity.
This means that the cavity is not filled with a glue for fixing the temperature sensor within the metal tip. As the metal tip is relatively long, i.e. at least three times, preferably five times longer than the diameter of the metal tip, there is a large contact surface between the metal tip and the tissue of the patient.
The probe body has a tubular plastic part and an elongated metal tip. The metal tip comprises a substantially tubular portion and a closed end. The temperature sensor is mounted at the closed end. Thereby, the temperature sensor is separated from the probe body by the cylindrical portion of the metal tip. The cylindrical portion is heated by contact with the patient""s tissue. A temperature gradient thereby is avoided or reduced. The whole metal tip is in contact with the tissue of the patient and is thereby also heated. As the heat capacity of the human body is extremely large compared to the heat capacity of the metal tip, the metal tip is heated without substantially cooling the patient""s tissue. The heating means of the patent U.S. Pat. No. 4,183,248 are replaced according to the present invention by the tubular portion of the elongated metal tip, which is heated by direct contact with the tissue of the patient. The tubular portion of the elongated metal tip forms a thermal isolation between the closed end of the metal tip with the temperature sensor and the remainder of the probe body, which avoids thermal energy collected by the tip being conducted towards the housing of the thermometer.
The temperature sensor is preferably made substantially flat, is positioned inside the metal tip of the probe body and preferably has a thermal time constant of less than 4 sec in still/not moving air. Thermal time constant is defined as the period of time when the temperature of the sensor reaches 63.2% of the temperature difference.
The metal tip of the probe body preferably has a length of at least 10 millimeters (mm), preferably about 12 to 15 mm, and a diameter of about 3 to 4 mm. The probe body should be formed as long as possible. It should, however, be ensured that the entire contact surface of the metal tip remains in contact with the human tissue.
The metal tip preferably has a thickness of less than about 0.12 mm.
The temperature sensor is arranged at the top of the metal tip and is preferably fixed thereto by a drop of glue, preferably an epoxy resin with good thermoconductivity. The remainder of the cavity formed by the metal tip is free from glue, i.e. only filled with air or a gas or another material having a low thermal capacity. The closed end of the tip forming its top comprises a substantially flat portion and a substantially cylindrical portion.
The metal tip is usually made of a metal, for instance stainless steel. The metal tip could, however, be formed of any other suitable material with sufficient thermal conductivity.
The thermometer comprises usually switch means for turning on/off and display means for indicating the temperature. The switch can be manual or automatic (e.g. in combination with a box or a movement sensor) and the display can be integrated in the housing of the thermometer or can be arranged at a remote location.